Migration: how many, what kind, and why it matters

This post is an introduction to a planned series of posts (some by me, some perhaps by others) that explore questions related to how many people might move under various changes that lead towards open borders (locally or globally). The goal of the current post is to explain why I consider the question extremely important. A subsequent post will take a somewhat opposite stand: namely, try to sketch a case for open borders that is independent of how many people might move. Later posts will look at specific policy changes, some of them realistic and others less so, and estimates of what might happen under these. Another area I plan to explore is the question of what the most critical bottlenecks are to large-scale migration (the most obvious candidates are housing and infrastructure) and what limits they set on migration rates.

A while back, I wrote a blog post critical of what I called “economic determinism”: the idea that migration flows are determined completely by economic conditions and that legal barriers to migration have practically zero effect on the magnitudes of migration flows. There are factors other than economic conditions and legal barriers to consider as well, of course: factors such as cultural connections between the sending and receiving country. Alvaro Vargas Llosa’s recent book Global Crossings: Immigration, Civilization, and America drove this point home for me. So, I guess the position I am broadly critical of could be expanded beyond economic determinism to what I might call “restriction irrelevantism”: the idea that restrictions imposed by nation-state governments on migration are largely irrelevant in terms of their effect on the magnitude and nature of migration flows.

Vargas Llosa is definitely not an economic determinist, but whether or not he’s a restriction irrelevantist remains to be seen. This article seemed to suggest that he might be, but op-eds tend to be oversimplifications, and his book, which I haven’t completed reading, may offer a more nuanced picture. I was nonetheless somewhat disappointed by the fact that Chapter 3 of the book, titled “Why They Move” and otherwise excellent at considering the motivators for migration, gave short shrift to the idea that different degrees of restrictionism in different target countries might significantly affect people’s decision of whether or where to migrate.

In any case, this blog post is not about the somewhat extreme position of restriction irrelevantism, which may or may not have real proponents. The majority of proponents and opponents of open borders do not subscribe to restriction irrelevantism. Rather, I think there’d be general agreement that millions more would move, temporarily or permanently, under open borders. But “millions” is a vague term. It could range from an extra five million people over the next two decades to an extra 100 million migrants (many of them temporary) within 2-3 years of global open borders (the main data for how many would move under open borders in terms of the stated preferences of potential migrants are the polling data on migration, which suggest that over a billion people want to go to other countries temporarily or permanently, and about 500-700 million people think they would make long-term moves if they were allowed to). One could come up with a fairly diverse (albeit less so) range of estimates for the number of people who might move under a more targeted open borders regime. For instance, if the United States announced open borders for Haiti (population about 10 million), one might envision a scenario of anything between 2 million people moving to the United States over the next year to a roughly equal number moving to the United States over the next two decades.

The closer the proposed change is to the status quo, the less likely the range of disagreement, but since we are talking here about relatively radical ideas such as open borders, there could be considerable divergence of opinion.

Closely related to the question of how many is the question of who. Many arguments offered by open borders advocates rely on the crucial idea that migrants self-select, i.e., it is not all that easy to migrate to a new land, and therefore migrants are not representative of the populations they hail from, but rather, are selected for positive qualities. As BK has pointed out in the comments (see for instance here and here) you can’t have your cake and eat it too for selectivity: if your estimate says that 25% of the population from region A will move under open borders, you can’t assume that the average migrant who moves will be selected to be in the top 1% of people from region A.

While the precise economics behind double world GDP estimates tends to be complicated, an important point is that all the estimates of huge economic gains also predict that this happens through large numbers of people moving. If, in fact, large numbers of people do not move, then at any rate these specific estimates are not applicable (there may be other mechanisms by which world GDP might increase considerably, such as innovation, but at any rate the specific estimation exercises of the papers would be flawed if very few people moved). For instance, in his blog post about John Kennan’s paper on Open Borders, Nathan Smith writes:

In predicting the volume of migration, Kennan does not assume that humans are strict homini economici who will go wherever they can earn the most. He writes:

One might initially expect that in a world with open borders, everyone would move to the most productive location. But this ignores the strong attachment to home locations that is evident in the data.

He takes this into account by making the migration decision probabilistic, such that the proportion of people who stay in a country is the same as the proportion of the rich-country wage that is paid in that country. For example, if there are open borders between the US and Puerto Rico, and Puerto Rican wages are 2/3 of those in the US, then 2/3 of Puerto Rican adults would stay in Puerto Rico. This roughly fits the data in that particular case, but there is no theoretical motivation for that particular functional form. Relative to a homo economicus model in which everyone who could earn more elsewhere migrated, this assumption causes Kennan to understate the economic benefits of open borders. On the other hand, it also makes Kennan’s version of open borders less scary than it would be if all who stood to gain economically from migration migrated.

This still posits a large number of people who’d move under open borders. Nathan writes later (emphasis mine):

Now, two big things we would like to know about open borders are (a) how many people would move, and (b) how much would world GDP actually increase. If I’m not mistaken, Kennan could easily derive estimates of these things from his model. But he doesn’t. He doesn’t tell us how world GDP would rise under open borders, in the short or the long run. He doesn’t tell us how many people would move, or where they would come from. I think Kennan’s model implies a short-run increase in world GDP of about 65%, and I’m pretty sure in the long run world GDP would double. Since the increase in the effective labor supply comes from growth in the populations of rich countries where labor productivity is high, I think Kennan’s model implies that rich countries’ populations would more than double due to immigration under open borders.

Another related concern is swamping. One of the main concerns of people ranging from hardcore restrictionists to moderate pro-immigrationers and even some who identify as being pro-open borders is that true open borders would lead to very large numbers of people moving over short time periods in a manner that would strain housing, electricity, water supplies, and other infrastructure in the countries receiving the immigrants. The typical response is to point out that (i) borders can be opened somewhat gradually to minimize the possibility of an immediate flood of people (see here for instance), and (ii) in any case, migration flows will tend to be self-regulating and people are likely to plan ahead at least somewhat before making a big move. Evaluating the legitimacy of swamping as a concern is part of the reason why it’s important to get a handle on how many might move under migration regimes that move the needle considerably towards open borders.